All publications and patent applications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed inventions, or that any publication specifically or implicitly referenced is prior art.
Micro-electro-mechanical deformable mirrors (“MEMS-DMs”) are useful for wavefront manipulation in imaging and beam forming systems. High degree-of-freedom mirrors are used to correct for random aberration from sources such as atmospheric turbulence. These mirrors are distinguished by the use of a large number of actuation sites, and can adopt complex surface shapes. Low degree-of-freedom mirrors can be designed for specific wavefront correction such as focus control. These mirrors cannot deform arbitrarily, but are intended to provide a variable amount of specified wavefront correction. In some applications a high degree-of-freedom mirror may be suitable to provide the same correction that a low degree-of-freedom mirror offers, but at the expense of a significantly more complex interface and control scheme. For applications such as endoscopic imaging systems, a simple interface and fast, precise wavefront correction for focus control and spherical aberration correction is desired.
Previously we described circular silicon nitride membrane mirrors for focus control (P. Himmer and D. Dickensheets, “Micromachined silicon nitride deformable mirrors for focus control”, Optic Letters, Vol. 26, No. 16 (Aug. 15, 2001) and “High speed, large deflection deformable mirrors for focus and spherical aberration control”, IEEE/LEOS Optical MEMS, Lugano, Switzerland (2002)). There mirrors employed two annular actuation zones to achieve spherical aberration free focus control, and also offered the possibility of correcting up to two waves of spherical aberration, measured at λ=660 nm. Use of these mirrors in an optical system necessitates the use of a beam splitter, if the incidence angle of the beam is to be normal to the mirror surface. Using the circular mirror with an incidence angle other than 90 degrees can eliminate the need for a beam splitter, but introduces off-axis aberrations.